Pneumatic conveyors are widely used today for transferring grain and other types of granular material. For example, such devices can be used for transferring grain from a storage silo to a delivery truck, a laborious and time-consuming task which was otherwise accomplished by shoveling. Such pneumatic conveyors generally include a cyclone separator having a tangential material inlet and a bottom axial material outlet. The suction side of a blower is connected to an axial air inlet in the top of the separator. The high pressure side of the blower in connected to a rotary valve which is connected between the material outlet of the separator and a line leading to the point of discharge. Such devices have been mounted for mobility and adapted for use with power take-off attachments on tractors to facilitate portability and use in unloading various silos on a farm, for example.
Pneumatic grain conveyors of this general type have been available for years under the name HANDLAIR from Christianson Systems, Inc. of Blomkest, Minnesota, the assignee hereof. See U.S. Pat. Nos. 4,433,946 and Des. 271,105.
Heretofore, however, such pneumatic conveyors have tended to be relatively noisy. The noise is primarily due to the flow of high pressure air from the discharge side of the positive displacement air pump or blower, the intake side of which is connected to the cyclone separator, and thus tends to receive air dirty and laden with dust and other foreign particles which are too large for centrifugal separation with the grain or other granular material being handled. Discharge silencers for rotary blowers have been available heretofore, however, the silencers of the prior art have used chambering and/or absorptive materials which tend to become clogged, particularly when used with dirty air. As a result, the silencers of the prior art quickly become ineffective, and are thus not suitable for use with pneumatic grain conveyors. Heretofore, there has not been available a silencer for pneumatic grain conveyors which is self-cleaning and effects noise reduction without the need for absorptive material that would otherwise become clogged and required cleaning and/or replacement and thus interruption in operation, down time, and expense.
A need has thus arisen for a self-cleaning silencer which is particularly adapted for use with a pneumatic grain conveyor.